Chromium oxides can be used as catalysts in a reaction for exchange or reorganization of halogens in compounds which are hydrocarbon-based or of halogenated hydrocarbons.
The properties of these catalysts can be, inter alia, modulated by the methods for producing them and by the compositions thereof.
Chromium oxide-based catalysts are generally produced by precipitation of salts using alkaline agents, followed by washing, drying and calcining steps. By way of example, mention may be made of document U.S. Pat. No. 6,337,299 describing a process for obtaining a fluorination catalyst comprising a chromium oxide produced by precipitation, followed by steps of drying, compression in the form of granules and calcining.
Chromium oxides can be produced in various crystalline or amorphous forms.
Chromium oxide-based fluorination catalysts may comprise doping agents such as, for example, nickel (FR 2 684 567), vanadium, magnesium or zinc (FR 2 713 633) or indium, gallium, cobalt, nickel, zinc and aluminum (U.S. Pat. No. 6,433,233).
The preparation of catalysts based on doped chromium oxide is generally carried out by coprecipitation. After drying and calcining, the solid is often subjected to a step of treatment with HF gas or with a fluorinated gas, and/or of activation.
The preparation methods as described above are not entirely satisfactory. This is because the coprecipitation method is limited by the solubility range and is consequently not very flexible. It also results in a heterogeneous composition and/or solids with specific surface areas that are not very highly developed, thereby limiting catalytic performance levels. In addition, the abovementioned methods consume large amounts of water and energy.
The applicant has now developed a process for preparing a chromium-based solid which does not have some or any of the drawbacks of the methods described in the prior art.